With the progress of technology, various loads, such as light emitting diodes (LEDs), driven by power and having various functions have been developed. These loads satisfy people having various requirements and contribute human's daily life, and thus enable people to have more convenient life.
Generally speaking, the loads are connected with a power supply circuit so as to obtain power for operation from the power supply circuit. In case that the load is an LED, when the LED is applied to a device, such as an LCD panel, the LED is connected with a power supply circuit to be driven by the power supply circuit and emit light. The power supply circuit mainly includes at least one power conversion circuit and at least one switch circuit. The switch circuit is conducted or shut off according to a switch signal outputted from a system circuit of the LCD panel. The power conversion circuit is connected with the LED and the switch circuit, and is used to convert the received power, such as the commercial power, into a driving voltage required by the LED for driving the LED to emit light when the switch circuit is conducted.
Certainly, the power supply circuit can be connected with multiple sets of LEDs to drive the multiple sets of LEDs to emit light at the same time. To enable the power received by each set of the LEDs to be precisely controlled so that the brightness of the LEDs can be maintained at a predetermined value, the power supply circuit includes a plurality of power conversion circuits and a plurality of switch circuits, which are corresponding to the multiple sets of LEDs. The plurality of switch circuits are simultaneously conducted or shut off according to the switch signal outputted from the system circuit. Each power conversion circuit and each switch circuit are connected with a set of LEDs, respectively. When the plurality of switch circuits receive the switch signal and are simultaneously conducted, each power conversion circuit converts the received power into the driving voltage required by the corresponding LEDs, so that the brightness of each set of the LEDs can be maintained at a predetermined value.
Although the conventional power supply circuit can drive the multiple sets of LEDs through the plurality of power conversion circuits and the plurality of switch circuits, it still has some drawbacks as the plurality of switch circuits are simultaneously conducted or shut off. For example, when the plurality of switch circuits of the power supply circuit are simultaneously conducted or shut off, the input current in the power supply circuit is abruptly increased or decreased, and thus a significant audio noise is generated in the power supply circuit. Further, when the plurality of switch circuits are simultaneously conducted, since the input current is abruptly increased, a great inrush current is generated in the power supply circuit. As a consequence, the power supply circuit may shut down or have unexpected mal-operation, and even more, the electronic components in the power supply circuit may be damaged.
Therefore, it is needed to provide a power supply circuit and a control method thereof to obviate the drawbacks encountered from the prior art.